Pity he's left here gloomy, having lost second round (7)
I believe the answer is:
remorse
'pity' is the definition.
(I've seen this before)
'he's left here gloomy having lost second round' is the wordplay.
I cannot quite see how this works, but
'second' could be 'mo' (both are short periods of time) and 'mo' is located in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for remorse that I've seen before include "Gnawing pain of conscience" , "Pity" , "Contrition for wrongdoing" , "compassion" , "it may bite" .)